FrSky Electronic Co., Ltd. of Jiangsu, China is a manufacturer of 2.4GHz radio control equipment.
The systems use the ACCST (Advanced Continuous Channel Shifting Technology) proprietary protocol which has been tested and found to be very robust also in noisy environments. FrSky also offers Futaba FASST-compatible receivers which are not in scope of this article.
|Disclaimer: this is not official FrSky documentation and FrSky has not been involved in its production. All information in this Wiki is provided as-is and no warranty, implied or otherwise, is made as to its correctness. Mention of vendors is not made as an endorsement. Use at your own risk!|
- 1 Overview of the System
- 2 Transmitters
- 3 Receivers
- 3.1 "V8" receivers
- 3.2 "D" receivers
- 3.3 "D16" Receivers
- 3.4 Summary: Transmitter - Receiver Interaction
- 3.5 Receiver Feature Overview
- 3.6 A Word on Receiver Port Naming
- 3.7 A Word on Channel Naming
- 3.8 Understanding RSSI
- 4 Future Development
- 5 Telemetry
- 6 Hub-Based Sensors
- 6.1 FBVS-01 Battery Voltage Sensor
- 6.2 FLVS-01 Lipo Voltage Sensor
- 6.3 FLVS-02 Lipo Voltage Sensor
- 6.4 FAS-40 Current Sensor
- 6.5 FAS-100 Current Sensor
- 6.6 FGS-01 Fuel Gauge Sensor
- 6.7 GPS-01 GPS sensor
- 6.8 FVAS-01 Variometer Sensor
- 6.9 FVAS-02 Variometer Sensor
- 6.9.1 Connecting the FVAS-02
- 6.9.2 Outputs
- 6.9.3 Included Cables
- 6.9.4 Variometer Sounds
- 6.9.5 Bridging between S.Port and "old style" Data Port
- 6.9.6 Using the FVAS-02 with the D4R-II Receiver
- 6.9.7 Using the FVAS-02 with the D6FR Receiver
- 6.9.8 Using the FVAS-02 on Telemetry-modified 9X with ER9X firmware
- 6.9.9 Firmware Bug
- 6.10 TEMS-01 Temperature Sensor
- 6.11 RPMS-01 RPM Sensor
- 6.12 TAS-01 Triaxial Acceleration Sensor
- 7 S.Port Sensors
- 7.1 Compatibility with "D mode" receivers
- 7.2 S.Port Sensor Firmware Upgrades
- 7.3 Exposed Connectors
- 7.4 FVAS-02 Sensor
- 7.5 FAS-40S Current Sensor
- 7.6 FAS-100S Current Sensor
- 7.7 SP2UART Analog Adapter
- 7.8 FLVSS Voltage Sensor
- 7.9 GPS (FrSky GPS V2 for S.PORT)
- 7.10 Air Speed & RPM Sensor
- 7.11 Third Party Sensors
- 8 Example Use Cases
- 8.1 Flight Pack Voltage Measurement
- 8.2 Power Consumption and Voltage Measurement
- 8.3 Telemetry in Gliders
- 8.4 GPS Position
- 9 Useful Links
Overview of the System
FrSky is notable for two things:
- Low-cost yet high-performance equipment including telemetry functionality
- Woefully inadequate documentation often consisting of little more than poorly translated leaflets
The former and latter combined make the system hard to understand and to utilize to its full potential, especially by newcomers to the field. This Wiki seeks to serve as a collection point for information gathered from FrSky themselves, various web forums, and users of the system. At this point in the game the FrSky system requires the user to do some research and be willing to experiment. If you want an off-the-shelf-system with proper documentation you should probably look for other alternatives from manufacturers such as Spektrum, Futaba, Multiplex, Jeti, or Graupner/SJ.
Is FrSky For You?
This quote by user "jj604" on RCGroups.com sums it up nicely when he says:
|"You have to understand this is a small entrepreneurial Chinese company with an innovative product. When you add the non-English speaking background to the rapid pace of development and lack of any overarching technology roadmap you just have to expect difficulties. This is not Spektrum or Apple territory. [...]
"This stuff appeals to the clever technical folks because of its high functionality to price ratio but the downside is that the documentation is written by engineers who tend to focus on how things work rather than what you have to do to make them work - and is not always slanted at users. [...]
"You aren't going to find it easy going. [...] For example FrSky have obsoleted many of their receivers faster than Spektrum can bring out basic sensors for theirs! [Add to that] the fact that FrSky CURRENTLY have no less than three totally different simultaneously operating data protocols for their telemetry system.
"[...] I can tell you this FrSky system is fantastic quality and very very good value for money. But if you think a Taranis is going to be as simple to set up as a DX5 - it is simply not true. FrSky is the Linux of radio systems. Extremely good value, powerful and elegant but you do have to work at it."
FrSky offers a number of radio modules that can be added to third-party manufacturers' transmitters. This section only lists the telemetry-capable "two-way series", also called "D"-mode. The previous generation, called the "V8"-mode modules, is discontinued and will not be discussed in this Wiki.
The DJT module is compatible with the JR specification of transmitter modules. It can be added to transmitters with JR-compatible module bays.
These include the Graupner MX-22 and MX-24 (non-HoTT), the JR X9303 and PCM 9XII, the Turnigy 9XR, and the popular 9x family of transmitters marketed under the Eurgle/FlySky/Imax and other brands and sold by Hobbyking. (Note: Some 9x radios have extra plastic around the pins and the DJT will not fit without modifications. Some users grind the plastic on the 9x, and others modify the plastic on the DJT.)
The DJT uses two LEDs on the module faceplate to show the operating status:
|Green LED||Red LED||Operating Mode|
The module will also emit an audible beep sound when in range check mode.
The DFT is compatible with the Futaba module bay specification and can be used with suitably-equipped Futaba and Hitec transmitters. (Hitec mounts their Futaba spec modules upside-down, so you may want to flip the antenna mount on your DFT when using it in a Hitec radio.)
LED indications on the DFT module are the same as listed for the DJT module, above.
The DHT is marketed as a Do-It-Yourself module and comes without a casing, unlike the DJT and DFT modules. It can be used with any transmitter but installation requires opening the transmitter case and soldering 3 wires to the transmitter. It also requires installation of a 2.4 Ghz antenna, and the mounting of some switches. The module is normally installed inside the transmitter case in a convenient spot. Such a spot can be hard to find in some transmitters, particularly the 9XR where the module bay is the only real option.
The 3 wires are ground, switched power and the PPM signal. Often times these sources can be found at the trainer port of most older radios. Some newer Spektrum radios may lack the PPM signal that is required.
The current version of this module is 2 way, that is it can be used to connect to the "old" V series receivers and to the newer D series. There is a switch that enables selection between the two. The module provides for a telemetry interface when in D mode.
Herunder is the status of the unique transmitter's led :
The DHT-U is an all-in-one radio and telemetry display module that interfaces to the transmitter in one of two ways:
- the 5-pin connector inside the module bays on JR, Spektrum, Hitec, Futaba, and other transmitters
- the trainer port on Futaba transmitters
It can be clamped to the transmitter's handle and operates independently of a radio module that may be integrated in the transmitter. It does require an empty module bay to be able to access the connector inside it so it cannot be used alongside a radio module installed in the module bay. The DHT-U displays telemetry information in much the same way as the FLD-02. Units with firmware version 2.3 or later are capable of logging telemetry data to an SD card placed in the integrated card slot. Be sure to read the release note of the firmware as some functionality has been removed with the V2.3 upgrade!
All the "D" series modules mentioned above are also backward-compatible with select "V8" series receivers, see the "V8" receivers section.
This module fits the same Graupner/JR-style module bay as the DJT and supports three selectable operating modes:
- D8 (existing 8-channel two-way mode)
- D16 (new 16-channel two-way full duplex transmission, also sometimes called "X"-mode)
- LR12 (new 12-channel one-way long range mode). This is said to have approximately three times the range of the current "V8"- and "D"-series when used with the new "LR"-series receivers.
The module has a serial interface as well as a new connector called the S.Port (Smart Port). The serial RS232 interface continues to support the FLD-02 display and accepts the FrUSB-3 adapter for firmware upgrades. The Smart Port connector is intended to be used with more advanced telemetry displays, for example the new Smart Dashboard. Firmware upgrades can also be performed via the Smart Port using a suitably modified cable (see S.Port Sensor Firmware Upgrades).
The module auto-detects whether PPM or PXX mode should be used towards the transmitter. With PXX it offers features like mode selection, bind, model match, range check, failsafe, etc. directly from the transmitter (if supported by the transmitter software). Another advantage of the module is a reduced latency, down to 1/3 that of the DJT as claimed by the manufacturer.
If PPM is detected from the transmitter the over-the-air protocol can be selected between D8/D16/LR12 by DIP switches on the XJT module. In PPM mode the module supports transmission of up to 12 channels, provided the transmitter itself is able to provide them to the module.
A noteworthy limitation of the XJT radio module when used in conjunction with an X8R receiver (in the new D16-mode) is that data from Smart Port sensors is NOT made available via the serial RS232 interface and thus cannot be displayed on an attached FLD-02 display. An attached FLD-02 will only display the RSSI and internal voltage values from the receiver, nothing else. This situation is unlikely to change until the release of the Smart Dashboard which attaches to the transmitter module via the Smart Port. When used with an "old" D8 receiver (in D8-mode) the XJT will output all hub sensor data via the serial port and thus behave exactly like a DJT module with respect to sensor data. See also the section titled Caveat with S.Port Sensor-Based Telemetry.
The Taranis transmitter (officially called the X9D) is a full-featured transmitter running an adapted version of the OpenTX software and provides up to 16 channels using the internal "XJT" module. Additionally it has an empty module bay on the back that accepts JR-style modules. The internal and external modules can be turned on and off via the model memory. The external module allows users to add other RF systems to the Taranis; like UHF, FASST, Spektrum, etc. The transmitter includes a technology called "Receiver Match" which is an equivalent of JR's "Model Match". This safety item ensures that you do not attempt to use the wrong memory with your model. The Taranis also has a built-in USB interface and a micro-SD memory card slot.
The Taranis integrates with Companion9X – a free computer program that is a transmitter setup buddy. Companion9X (Windows/Mac/Linux) is used to set-up models with the wizard, save, edit, and share your models and settings as well as simulate your transmitter or model setup. A simple USB connection allows you read and write your data from the transmitter.
Preproduction models were displayed at the Toledo 2013 show and have generated a great deal of anticipation. Delivery of the Taranis transmitter started in calendar week 25, 2013.
Documentation of the OpenTX software as delivered with the Taranis transmitter is available on the OpenTX Google Code Wiki.
A very comprehensive FAQ-thread on the Taranis can be found on RCGroups: .
Production Batches of the X9D Taranis
Production was divided into two batches; called 'A' and 'B'. The first, A, had some quality control problems especially with the gimbals. Replacement gimbals were offered as a retrofit under warranty.
The only externally placed identification feature is a silver sticker on the module cover on the back of Taranis. It shows the serial number in the format X9DxxxxxxA01 or X9DxxxxxxB01. A01 and B01 refer to the two produced batches of the Taranis. Unfortunately, with the module cover obviously being removable, those numbers can be swapped around between different transmitters, so used buyers beware. All transmitters sold by distributing dealers after mid-November 2013 are supposed to be B-batch models.
There is also a small white decal in the module bay, visible after removing the module cover or any module that may be installed. It shows distribution info. For example, in the label “A01 US AH 28/10/2013” A01 refers to the continent of North America, US refers to the country of United States, AH is short for Aloft Hobbies, and 28/10/2013 is the production date. Note that the A01 in this case does NOT denote this transmitter being an A-batch product.
In November 2013 an upgraded version of the Taranis, called the X9D+, was announced. Key new features include haptic (vibration) feedback, upgraded sliders, dual-color LED backlight grey-scale display, and a 6-position replaceable encoder. Frsky have announced they will carry a retrofit pack to upgrade X9D transmitters to X9D+ specifications. The new transmitter modelis expected to be available around December, 2013.
Summary: Transmitter - Radio Module Interaction
With the exception of the Taranis radio the FrSky system relies on FrSky radio modules operating in 3rd party transmitters. This section provides information about the communication between the radio and module.
The DJT, DFT, and DHT modules currently accept only a PPM signal as input. PPM is a well-known standard used by all radio manufacturers for the past 40 years or so. Pretty much every module-based radio on the market uses PPM as the protocol. The modules will only take up to 8 channels, because the "V"- and "D"-mode protocols they can transmit only support up to 8 channels anyway.
The new XJT can accept either PPM, or the new FrSky PXX protocol. Like PPM, PXX is a protocol that is ONLY used between the radio and RF module; not between the RF module and receiver. Its purpose is to allow communicating things other than just servo positions to the module. The good old analog PPM works, but can only send servo positions, which nowadays is quite limiting.
PXX currently allows passing transmit mode (D16, D8 or L), region code (to follow different countries' radio regulations), model number (for receiver match), failsafe mode and positions, as well as initiating binding and enabling range check mode in addition to up to 16 channels. These are features that are present in non-module based radios but generally not in radios relying on an RF module.
When PXX is used between the transmitter and XJT, all these things can be set on the transmitter, stored in the model settings, and the info is transmitted to the module when needed.
When the XJT receives PPM it still needs to be told which RF protocol to transmit with, and one needs to put it in bind or range check modes when needed, so there are DIP switches and a push button for that, just like on the DJT/DFT/DHT modules. From prototype testing it will accept up to 12 channels on the incoming PPM signal. Some transmitters allow 16 channels to be transmitted via PPM but this is not tested and not officially supported by the XJT.
- to send 16 channels, you need a protocol that supports that many (D16), a module and receiver that support that protocol (XJT and X8R), and a way to send that many to the TX module from the transmitter (PXX).
- to send 9 channels you need a protocol that supports that number (D16 or L), a module that supports those (XJT), a receiver that does too (X8R or L9R), and a way to send 9 channels to the TX module (either PXX or PPM from the above info).
- to send <=8 channels you can use any pair that has at least one protocol in common.
PXX is implemented in OpenTX software, so it is available on the Taranis (which is a given since it uses an internal XJT radio), as well as any other transmitters OpenTX can be run on. It is also implemented in the er9x software. If someone wants to grab the code and implement it on other radios they're free to do so since both OpenTX and er9x are free and open source software and available to everyone. More information on both software packages as well as other projects related to Open Source r/c radio can be found on .
The (Turnigy and other brands) type 9X transmitter can be modified to display telemetry on its main screen. It can be done with an internal module (DHT) or external one (DJT). There are a few ways to do that all documented here: http://openrcforums.com/wiki/index.php/How_to_modify_your_9x_to_support_telemetry The wiring for telemetry reporting also requires that a few connections to switches be modified on the transmitter. Thus the transmitter will REQUIRE a specific firmware to be functional. Such firmwares are for example ER9X, Open9X, or OpenTX that will provide for the telemetry data, info and display and also for the rerouting of switches. The firmware option "FrSky telemetry" should ONLY be set if the actual hardware modification has been done - otherwise the throttle hold and aileron dual rate switches will become inoperable! For more details on such firmware and what is required refer to the OpenRC site as well.
Once the display is wired, if you use ER9x you will need to set up parameters: Use this page for info on ER9X: http://openrcforums.com/wiki/index.php/Er9x_user_guide To see the correct battery voltage of the battery connected directly to the receiver (without a BEC or similar), the "channel parameter" has to be set at 13.2v
An option available to users who would like telemetry information on their 9x system without having to solder SMD component-size connections is the "9x TelemetrEZ" by Smartieparts: http://www.smartieparts.com/shop/index.php?main_page=product_info&cPath=3&products_id=337 This add-on board will not physically fit the newer Turnigy 9XR receiver. There has been some discussion on releasing a board that will fit both transmitters, but no product has been yet released. The only option for 9XR users is the one listed above which requires soldering.
Turnigy is working on bringing an advanced transmitter to market that will be using the 9XR mechanicals and is to be called the "9XR Pro". It will incorporate a new development based on the Sky9x board and is expected to boast a number of features that are currently only available in the Taranis; including telemetry support, voice output, SD card slot, and a USB interface. A tentative release date of late 2013 is expected.
FrSky has several different generations of receivers which while all using the same ACCST radio protocol are only partially compatible.
All receivers with names beginning with "V..." do not support telemetry. (Note FrSky officially calls them "V8" even though not all receivers are 8-channel receivers and not all their names start with "V8". All names DO start with "V...", though.) They can only receive commands from the transmitter modules and will not send back any information. All currently available V8-receivers function with both the "V8" and "D" series transmitter modules, but this isn't true for the older, discontinued V8 receivers.
If you are thinking of purchasing an older (maybe used) V8-series receiver to use with your "D" series transmitter module you should first check the table below or the FrSky V8 receiver page to verify it works in "D"-mode. Frankly, the FrSky receivers are cheap enough to make such a purchase decision seem questionable.
|"V"-mode Receiver Compatibility|
|Receiver||Channels||Compatible with "D"-mode transmitter?|
Note this table only lists the currently in-production "V8"-receivers. Discontinued models are not listed.
One of the "V8" receivers deserves special mention and this is the ultra-small VD5M. While not being telemetry-capable it can operate both in "V8" and "D" mode and continues to be the smallest available receiver for the FrSky ACCST system. At 2g weight (or less if removed from it's protective packaging) it is a great choice for ultra-micro and indoor models. The VD5M does not support failsafe and is intended for indoor use.
The non-telemetry receivers are a nice option for saving a few dollars. But the telemetry receivers offer RSSI, greatly enhancing flight safety and are highly recommended for larger or faster aircraft where crashing is not an option.
The "D"-mode Telemetry Receivers work with the "D"-mode Telemetry Transmitter Modules and the new FrSky transmitters. They are capable of transmitting back telemetry information to the transmitter. However, their support of telemetry varies in important details and these details need to be understood for successfully using telemetry.
Common to all "D"-mode receivers is their capability to transmit Receive Signal Strength Indication (RSSI) and two voltage values (A1 and A2) back to the "D"-series transmitter.
RSSI is an important safety feature as it will let the operator know the reception quality of the receiver inside the model. As the RSSI level drops the operator will know that the model is close to flying out of range or is approaching an area of signal disturbance, or for any other RF quality issues. An alarm will be sounded as a certain level is reached to warn to pilot prior to loosing control of their aircraft. This saves models and is good for the hobby in general. The system should not sound an alert during normal flight operations. If you hear random beeping from your transmitter, you are OK, but you should check your antennas when you land. If you hear a steady alarm, you should land and inspect. If you hear a steady fast alarm, you should land ASAP as you are very close to loosing control of your aircraft, at which time your receiver will drop into your programmed failsafe option.
Internal voltage (A1) level reporting can be useful if the receiver is powered off its own receiver battery pack, such as might be the case in a glow-powered or glider model. If the receiver is fed off a battery eliminator circuit (BEC) the voltage level will always be what the BEC delivers, e.g. 5V. If using a BEC you can use the (A2) port to monitor the flight battery.
Battery Connection FrSky, like some other makes, does not have a dedicated "battery" port. You can plug in your battery to any open servo channel. If all channels are used, a "Y" extension can be used to add the battery to any channel. Do not plug servos or batteries into the A2 or data ports of any receivers.
|Range||Full Range (>1.5km)|
The D8R-II plus is a full range 8-channel receiver with two external analog telemetry ports (A1 and A2) and one digital data-stream port. The two ports on the side (labeled A1 and A2) can be used to connect FBVS-01 voltage sensors for monitoring external battery pack voltages. Under no circumstances should a battery be connected directly, without the voltage sensor, to A1 or A2 as the ports can only sustain a maximum of 3.3V. Jumpers are included with the receiver. If the two lower pins in the A1 socket are connected via a jumper the A1 value reported by the receiver will be the voltage level that is sensed across any of the servo connections 1-8 (which usually means the voltage provided to the receiver via the ESC connection).
The D8R-II plus is equipped with a digital data port to which a sensor hub FSH-01 can be connected. See the Sensors section below for more information.
The receiver's firmware can be upgraded by downloading the appropriate firmware image from the FrSky website and using the FrUSB-3 USB cable to upload it into the receiver. The internal hardware on this and the D8R-XP receivers is identical and in fact the XP firmware can be loaded into the D8R-II plus effectively turning it into a D8R-XP.
|Range||Full Range (>1.5km)|
The D8R-XP is a variant of the D8R-II plus receiver with one significant change: it supports the output of RSSI (PWM) and CPPM signals. If CH3 and CH4 are connected by a jumper, CH1 will output CPPM for CH1 through 8, and CH2 will output RSSI (PWM). The RSSI output is mostly useful for FPV applications where the operator cannot look at the telemetry display on their transmitter and would rather see the RSSI information via their OSD. Using CPPM the receiver can be connected e.g. to a flight controller with a single wire.
Other than this the D8R-II plus and and D8R-XP are identical.
|Range||Full Range (1.5km)|
The D6FR is a 6-channel receiver that supports only internal telemetry; i.e. it transmits RSSI and can measure two different voltages (A1 and A2). It does not have a data port and cannot be connected to a sensor hub. It is smaller, lighter, and consumes less power than the D8R receivers.
A1 is internal in the receiver and always measures the voltage supplied via any of the 6 servo connections; in most cases this will be the supply voltage provided via the BEC. A voltage sensor FBVS-01 can be connected to the A2 port and can be used to measure external battery voltage, e.g. of the main flight pack. No direct battery connection must be made to A2. Attention must be paid to the fact that no servo can be connected to A2 even though it is located next to and looks like a servo connector.
|Weight||5.8g / 5g (naked)|
|Range||Full Range (>1.5km)|
The D4R-II is the smallest and lightest telemetry-capable receiver in the FrSky range. It has only 4 channels, has one external analog telemetry port (A2) and one digital data-stream port with which it can be connected to a sensor hub FSH-01. The digital and external analog port share one single 4-pin connector for which a suitable cable is included. The A1 port is hardwired internally to report the supply voltage. Like the D8R-XP it can be configured to provide CPPM and RSSI (PWM) output. If CH3 and CH4 are connected by a jumper, CH1 will output CPPM for CH1 through CH8, and CH2 will output RSSI (PWM). If the FrSky product naming system weren't so confusing then this receiver would be called the D4R-XP...
|Range||Full Range (1.5 - 2.5km)|
The Delta-8 is a multiprotocol receiver supporting Hitec A-FHSS, Futaba S-FHSS, Futaba FHSS, and FrSky V- and D-modes. All these systems use the same RF chip and so it was possible to include them by firmware. The receiver has internal RSSI monitoring but does not have a data port, analog port, or S.Port so it does not support any external telemetry sensors.
A 4-channel version is expected to be released later.
All other "D"-series receivers are discontinued and are out of scope for this Wiki.
The "D16"-mode protocol was introduced in June 2013 with the release of the first products incorporating this technology, the Taranis transmitter and the X8R receiver. It is the designated successor to the "D"-mode protocol.
|Range||Full Range (>1.5km)|
This is a new 8/16-channel telemetry receiver. It can drive 8 channels in conventional mode and 16 channels via the SBUS port (which was previously only available on Futaba-compatible receivers). It also provides RSSI output and is Smart Port enabled. This receiver does not have analog (A1/A2) ports and the FSH-01 sensor hub cannot be attached to it directly. To attach hub-based sensors requires a data port to S.Port translation device, of which there is currently only one - the FVAS-02 variometer sensor.
The X8R is the first receiver that supports the new "D16"-mode protocol. It is also fully backwards compatible to the "D"-mode but not the "V8"-mode. It can be bound to all radio modules that can operate in "D"-mode (namely, the DFT, DJT, DHT, DHT-U) as well as the new "D16-mode" radio modules (namely, the XJT as well as the Taranis-integrated radio module). It does not support the new 12-channel, non-telemetry long range "LR12"-mode.
The receiver supports antenna diversity and is available with two different antenna styles; the usual two single-wire antennae, and a new style that has PCBs attached to the end of the antenna wires. These require significantly more space inside the model but are supposed to offer better reception and transmission (for telemetry) performance. The PCBs each measure 52mm x 9.5mm x 6.7mm and the wire length from the receiver case to the start of the PCB plastic cover is 83mm.
A six-channel version of the X8R receiver has been announced in November, 2013 for an expected December release date. This receiver is notable in that it will again feature an analog port for flight pack voltage measurement as was standard on the D8-mode receivers. Additionally, it will have pinout for six directly attached servos, SBUS (for all 16 channels), RSSI output, and of course an S.Port connector.
A four-channel receiver is also announced, but without any details or availability information.
Caveat with S.Port Sensor-Based Telemetry
With the D16-mode receivers and corresponding XJT transmitter module comes another cumbersome break in FrSky's product compatibility - Smart Port sensors. Basically, telemetry data from Smart Port sensors is transmitted using the S.Port protocol from the receiver back to the XJT transmitter module, which makes this data available ONLY via its built-in S.Port. Conversely, data from hub-based sensors is transmitted via the old style serial protocol in D8-mode only. There is no translation between S.Port and the old serial protocol. As stated in the discussion of the X8R receiver, the only way to facilitate this translation is by using the FVAS-02 variometer sensor. Currently the only device capable of displaying data received from S.Port sensors is the Taranis transmitter, at least until FrSky are releasing the Smart Dashboard.
Bottom line: if you are interested in sensor telemetry data do not invest into an XJT module and X8R receivers until the new Smart Dashboard is released, and if you are prepared to either replace your old sensors with new S.Port variants (most of which aren't yet available) or purchase an additional FVAS-02 just for the translation capability. Otherwise, stay with your D8-mode receivers and sensors and either the DJT module or use the XJT module in D8-mode.
Summary: Transmitter - Receiver Interaction
- the old V8FT, V8JT, V8HT TX modules could only transmit in V mode.
- the current DJT, DFT, DHT can operate in V and D mode.
- the new XJT can operate in D (aka D8), D16 and L modes.
- old V receivers can only receive V protocol.
- current D receivers can only operate in D mode.
- new V-II receivers can receive V and D protocols. When in D mode they do not transmit telemetry data.
- new X receivers can operate in D8 and D16 modes.
- new L receivers can receive only L mode (they do not support telemetry).
Receiver Feature Overview
This table shows the currently available "D" and "D16"-mode receivers and their features.
|"D"-mode Receiver Features|
|Receiver||Channels||Analog port(s)||Digital data port||Compatible sensors||CPPM output||SBUS output||External RSSI|
|D6FR||6||A1 (internal only) & A2||no||FBVS-01
FVAS-02 (variation only)
|D8R-II plus||8||A1 & A2||yes||all (via FSH-01 hub)||no||no||no|
|D8R-XP||8||A1 & A2||yes||all (via FSH-01 hub)||yes||no||yes|
|D4R-II||4||A1 (internal only) & A2||yes||all (via FSH-01 hub)||yes||no||yes|
|X8R||8 (16 via SBUS)||no||Smart Port||Smart Port only||no||yes||yes|
Several of the FrSky receivers feature a "case" made from printed cardstock material. This is a rather unorthodox approach to weight saving. Some users elect to remove the paper wrapping and instead use large-diameter heatshrink to insulate and protect the receiver electronics. This is advisable if the receivers should be used in potentially wet environments, such as boats or float planes.
A Word on Receiver Port Naming
FrSky have a somewhat confusing naming "convention" for the receiver ports. In short these different types exist:
- analog - these ports are variously called DA, A1, and A2. They consist of an analog voltage input that is limited to 3.3V and a corresponding ground pin. Some receivers have one of the two ports hard-wired internally to report the receiver supply voltage. In the case of receivers with two externally accessible ports, one of the ports can be shorted out with an enclosed jumper to provide this functionality (which is only useful if you don't use a BEC). The analog port accepts input e.g. from the FVBS analog voltage sensor or from the FVAS variometer sensor.
- digital - this port is variously called the digital port, digital data stream port, serial digital port, and digital sensor port. It accepts digital input directly from some sensors (e.g. the FAS and FVAS) or in all other cases from the digital sensor hub FSH-01 to which other sensors are connected.
- S.Port - this port is sometimes also called Smart Port and is the latest digital interface to be introduced by FrSky. It uses a single wire digital protocol which daisy-chains through all connected sensors. The latest FrSky radio modules also provide an S.Port. Do not confuse S.Port with S.BUS -- the latter is for servo connections!
A Word on Channel Naming
Some vendors (for example Spektrum) label the connectors on their receivers "Throttle", "Elevator" and so on. This is a convenience feature to enable the user to make the right connections without having to check the assignment in the transmitter. It is fine for simple applications but stops being useful when the user is required to understand that the second aileron servo has to go into the "Aux 1" output, which confusingly enough is labeled "Flaps" in the transmitter.
FrSky (and others) label the receiver ports with channel numbers. Depending on the transmitter it is up to the user to define which channel has which function. One common sequence would be RETA (rudder, elevator, throttle, aileron), but there is no hard and fast rule.
Users of OpenTX will be making those assignments in the "mixes" screen. In most cases the default template will have created 4 mixes with, for instance, CH1 being 100% rudder, CH2 being 100% elevator, and so on. Once the OpenTX approach to mixing is understood this is a far more useful concept.
RSSI (Received Signal Strength Indication) is an integral part of any "D" mode receiver and can be used without any external sensors. It is an important safety feature as it allows you to judge how the radio link is performing before a catastrophic failure occurs. It is of enough value by itself to warrant changing to a telemetry-capable system. User jj604 has written this section about RSSI as an integral but often misunderstood (due to lacking and unclear documentation) aspect of FrSky telemetry.
The DHT-U and FLD-02 display units as well as the upcoming FrSky transmitters can display RSSI values. There are two separate RSSI displays. The left one on the screen is the RSSI of the controlling signal from the Transmitter as seen by the Receiver and is called the RECEIVER RSSI. The right one is the RSSI of the telemetry signal back from the model as seen by the telemetry receiver in your Transmitter module and is called the TRANSMITTER RSSI. Don't be confused. The Transmitter RSSI is NOT the signal your transmitter is putting out - it is the signal from the telemetry module in the model. Lots of postings have them confused because of the naming used.
It is the first one - the left box - that matters to most of us since that is the signal strength the receiver in the plane is seeing from the transmitter. The signal the transmitter is seeing for the telemetry feed back from the plane is important to FPV guys and others but does not indicate the strength of the controlling radio link.
In normal operation the left value (Receiver RSSI) should always be greater than the right value (Transmitter RSSI) simply because the transmitter is optimized for high range. The receiver in the plane (which is the transmitter for the telemetry data) operates in more restrictive conditions (antenna orientation changes with plane movements, noise from onboard electronics, ...).
The FrSky system comes with some built-in alarms that you can set on the DHT-U or FLD-02 screen. How to set them and what they mean can be confusing. The important thing is that the default values for the RSSI alarms have been determined by FrSky and unless you really know what you are doing you should not change the numbers. You can only change the sounds and values of Alarm 1 and Alarm 2 in any case. Note that FrSky also sometimes call the alarm levels 0, 1, 2, 3 as Green,Yellow, Orange, Red for no useful reason. By default the alarm thresholds are set at:
- Green = No alarm = 0 beeps = Signal strength is strong
- Yellow = Alarm1 = 1 beep = Value 45 means signal strength is adequate
- Orange = Alarm2 = 2 beeps = Value 42 means model is at far, but safe, range
- Red = Alarm3 = 3 beeps = Value 40 means maximum range and indicates imminent failsafe (which actually occurs at about 37-38)
However since there are only three distinct alarm sounds in the whole system (1, 2, or 3 beeps) you may get the same sounds for RSSI alarms and any voltage (A1 or A2) alarms you have set.
Alarms are stored in the module, and not in the Rx. This means that if you have multiple models, and want to use different alarms for the different models, you will need to reprogram the alarms when you switch models.
Beware that there is a catch. Suppose you are at the limit of range and the telemetry receiving system in your transmitter module system loses the signal. Then a "feature" of the FrSky system is that the whole display freezes and displays the last good data. If you were just at the point of a control loss (Receiver RSSI) warning you will not get that warning. If you glance at the screen you might see an RSSI value displayed in the left box that is still safe but in fact it is not the current value but the one that was there when the link back from the model dropped out. So if you get a 3 beep alarm it pays to check which of the two RSSI values set it off. If it was the right hand one - don't trust anything you see on the screen until it starts updating again!
Setting sounds and triggers including turning an alarm off
There are different ways that can be used to set the alarms. The most common is using a FLD-02 attached to a module, or the facilities on the DHT-U, but it is also possible to program the alarms from computer and smartphone applications.
Using the scroll/push wheel move to the appropriate box until it highlights then push to select or change it. See the picture below. The way in which the FrSky system moves between the 3 digits of the value box or selects the box itself is a combo of pressing and scrolling right and is best understood by trial and error!
Applications known to work for alarm configuration:
- FrSky Alarm Configuration (from FrSky Beta Test section): http://www.frsky-rc.com/uploadfile/201209/20120903180326856.zip
- Third-party FrSky Config Program (from FrSky Beta Test section): http://www.frsky-rc.com/uploadfile/201103/20110328091659684.zip
- FrSky Dashboard: https://play.google.com/store/apps/details?id=biz.onomato.frskydash
Background: What actually is RSSI?
You don't need to know any of this to use the alarm system effectively but if you are curious...:
The received signal strength (RSSI) is actually not an absolute value like voltage or temperature but a number that indicates the ratio of the signal to some initial "good" value. It is in dB and is the same measuring system used for audio levels. For a fixed single system like the FrSky system we can treat the RSSI as an absolute value of strength since the "good" value is already chosen and fixed. The only unusual thing is that dB is a logarithmic measure, not linear. What this means is that any increase of 6 means the signal has doubled in strength. So a change of +12 in the RSSSI means the signal has increased in power by 4 times, by +18 means the signal has increased in power by 8 times, by +24 means the signal has increased in power by 16 times. Conversely if the RSSI goes down by -18 the signal power is 1/8 what it was.
For the FrSky system the RSSI should read about 110 at 1m and every time you double the distance between the transmitter and receiver, the RSSI level should drop by 6. That's why it goes down quickly at first then less and less as the model flies away since you have to double the existing distance each time to get 6 lower. Theoretically at about 100 meters you should get an RSSI value of about 70 in ideal conditions.
A good way to see this effect is to use Range Test mode (since RSSI still works). In range test mode the Transmitter module operates at 1/30 full power. Note where the beeps appear for all three levels. In real flight the distance will be 30x more.
Some receivers can provide RSSI externally, e.g. to connect to an OSD for FPV flying. See the Receiver Feature Overview table.
The RSSI is not output just as a voltage, it is a pulsed signal (PWM) with variable fill rate depending on signal strength. It can be averaged to a voltage easily using a Resistor-Capacitor filter as used in most OSDs. Connecting a voltmeter to the RSSI output already shows the RSSI as a variable voltage because it does the averaging and filtering inside. An example can be seen in this video: http://www.youtube.com/watch?v=IHjJ1QHV32Y
FrSky is preparing to bring to market a new range of products. The most notable components are listed below.
|Please note that this is all prerelease information and facts will only be known after the products are actually released.|
No reliable information on the Horus transmitter is available at this time.
The L9R seems to be the long range version of the X8R. It provides 9 channels (12 via the SBUS port) and also supports the Smart Port. It does not have telemetry functions as the LR12 protocol is one-way only.
There is a new generation of sensors arriving which do not require the FSH-01 sensor hub. The FVAS-02 is the first product which is already available. Hubless sensors will be a welcome improvement as they reduce cost, complexity, weight, and power consumption of a telemetry system.
The new sensors use the Smart Port (or S.Port for short). While the "old style" sensors were connected to a hub, the new S.Port sensors are daisy-chained onto a single-wire bus. The S.Port should not be confused with the similarly-named S.Bus -- the S.Port is used for sensors, the S.Bus is used for servos.
In general S.Port sensors require one of the new S.Port-equipped receivers. However, some sensors will include bridge functionality enabling a FSH-01 hub to be connected to them and the data thus being available over the S.Port. The FVAS-02 supports this bridge functionality.
FrSky Smart Dashboard
A new version of the rather limited FLD-02 telemetry display is also announced with a tentaive release date of late 2013. It is to feature a 2.4" color OLED screen, data logging capability via SD card, Smart Port, a USB interface, and - most importantly - a voice output/alert module. FrSky documentation references this as the FrSky Smart Dashboard although the name might change before its release to market.
This display is required to monitor telemetry data from Smart Port sensors. The FLD-02 will not show data from these sensors.
FrSky introduced 2-way telemetry functionality with the "D"-series radio modules and receivers. The system consists of so-called "core telemetry" functionality in the "D"-series receivers and includes a range of external sensors which can be connected to receivers equipped with a "data stream port". Please see the receivers section for a list of which receivers have a data port.
|Note that digital sensors cannot be connected to receivers without a data port. The voltage sensor FBVS-01 is an analog sensor which can be connected to all receivers that have at least one externally-accessible analog port (labeled A1 and/or A2). Refer to the Receiver Feature Overview table to see which receivers are equipped with analog and digital ports.|
FSH-01 Sensor Hub
The sensor hub is a small device which connects to the data port on receivers so equipped and offers a total of 8 ports to connect sensors to. There is one port for each sensor type FrSky offers, and a second temperature port. With older receivers, the hub was not powered through the data port cable but comes with a separate power supply cable which needs to be connected to a suitable power source (e.g. an open channel on the receiver, or the BEC). However if you are using a SmartPort Vario to bridge between the Sensor Hub and a SmartPort capable Receiver (such as an X8R), the Vario comes with a four conductor cable which does provide power to the Sensor hub.
The "volt" port is only used for the Lipo sensor FLVS-01 which can measure individual cell voltages. If you are using the simpler FBVS-01 battery voltage sensor it should be connected directly to the receiver's A2 port and not to the hub. So if all you want to measure is total battery voltage (via the FBVS-01 sensor) you do not need this hub.
The "temp" ports require a 100K NTC (Negative Temperature Coefficient) thermistor. The resistance of the thermistor is 100K at 25 degrees C and the resistance goes down as the temperature increases - hence the designation negative temperature coefficient. If you are going to use an aftermarket sensor, be sure it's a 100K NTC.
Here are some sample readings taking from a Sensor Hub connector to a Taranis via the High Precision Vario:
If you want to measure current flow and battery voltage (via the FLVS-01/02 and one of the FAS-xx amperage sensors) you also do not need the sensor hub. The FLVS connects to the FAS-xx and the FAS-xx connects to the receiver's digital data port directly. See also the use case section below.
It is important to understand that the FSH-01 parses and reformats the data coming from the sensors to a protocol the "D"-series receivers understand. The FSH-01 is firmware-upgradable. The user needs to make sure that the firmware revision in the hub is new enough to support whatever sensors are connected to it. It is generally a good idea to keep the hub on the latest released firmware.
Specifically, if you connect a voltage sensor FLVS-01 or FLVS-02 to the FSH-01 and your Tx does not display voltage information, you need to upgrade to V2.0 of the firmware. Consult the FSH-01 upgrade information on the FrSky website: http://www.frsky-rc.com/download/view.php?sort=&down=46&file=Upgrade%20How-to_FSH-01
FLD-02 Data Display
|Display||128x64 pixel white-backlit LCD|
The FLD-02 is an external display that connects to and is powered by the "D"-series radio modules via a cable. It displays telemetry data and can alert the pilot to telemetry values that have exceeded or fallen below certain defined thresholds via audible beeps. The monochrome LCD display is illuminated by white LEDs. It is a low-cost but somewhat limited workaround to the fact that no transmitter equipped with a FrSky radio module will be able to make use of the telemetry data without internal modification. It comes with a piece of Velcro which can be used to attach it to the transmitter body. A universal LCD mounting arm (product code: FMS) is also available from FrSky which can be used to help in attaching both the FLD-02 and the DHT-U.
As with the FSH-01 sensor hub it is important to keep the firmware version of the FLD-02 upgraded to the latest version. Otherwise sensor data may not be correctly displayed.
The FLD-02 comes with a cable to connect it to the DJT/DFT radio modules, but the polarity is not documented. On the DJT radio module, the black wire goes into the bottom connector (marked GND). When viewing the FLD-02 from the FRONT (display facing you), the black wire should be on the right.
The FLD-02 receives its operating power via the cable from the radio module which in turns receives it from the transmitter battery. When powered on it will display two options, "Menu" and "Data". Clicking on "Menu" with the combined scroll wheel/push button on top of the unit will enter the settings dialog where adjustments can be made. In this dialog "OK" will save the settings made while "Back" takes you back to the top-level screen. entering the "Data" screen the unit displays up to four different screens of data, depending on which sensors are attached to the currently used receiver(s). There is no way to exit the "Data" screens other than turning the unit (and thus the entire transmitter) off. Apparently this is a safety feature to keep pilots from inadvertently leaving the data display during flight. This can get cumbersome if you are bench-testing your setup and need to make frequent changes to the settings.
Note that when setting up alarms each alarm setting needs to be saved via the OK button. Switching from one alarm to the next without hitting OK first will make the FLD-02 forget the settings just made.
The Blade setting in the Menu is used to specify the number of propeller blades when the optical RPM sensor RPMS-01 is used.
Users of the 9x and 9XR transmitters can avoid using the FLD-02 and modify the transmitters and DJT module internally to allow the software to make use of the telemetry data (e.g. in alarms or mixers). This modification requires soldering to SMD components. Transmitters are also available already modified, tested, and flashed with a choice of firmware options.
A distinct drawback of the FLD-02 display is that it is incapable of emitting beeps in response to variometer sensor input when used with the old FVAS-01. Thus the pilot does not receive information on the current lift conditions without looking at the display, which is rather impractical. To make use of the variometer information requires the new FVAS-02 sensor.
DHT-U Radio Module & Data Display
Telemetry Display on Smartphone or Tablet
Two Android apps have been written that enable display of FRSKY telemetry data, setting alarms, voice output and logging on an Android device. These apps are called FRS_Logger and Frsky Dashboard. Both are available from the Playstore.
The apps both use the Android device's Bluetooth capability to transfer the data between the transmitter RF module (DJT, DFT or DHT) and the phone.
The Bluetooth connection device is not commercially available and has to be constructed. It is usually fitted inside the transmitter. It is a simple build well within the capability of anyone with basic soldering equipment and skills, and can be built for around $10.
The BT device has an effective range of around 5m. The smartphone or tablet can be mounted on the transmitter and used with or without a headphone, or used by a helper who advises the pilot of pertinent information and enables him to watch the model at all times.
User-upgradable firmware is a fact of life with modern electronics, which for the most part are just miniature computers in disguise. It's a double-edged sword as companies tend to release less-than-perfect products that the consumer then has to nurse into usefulness. On the up side, bug fixes can be easily brought out and require no hardware modification nor sent-in parts to the manufacturer.
Upgrading the various FrSky products requires several different devices as follows:
|FHS-01, FLD-02, DFT/DJT/DHT||FUC-3 (FrUSB-3)|
|D4R-II, DF6R, D8R-II plus, D8R-XP||FUC-3 (FrUSB-3)|
|S.Port sensors||FrUSB-1 or FrUSB-3 with modification|
|Taranis||standard A to mini-B USB cable (included)|
Firmware images are available from the download section of the FrSky website. The software required for the operation of the FrUSB-2 and FrUSB-3 USB devices unfortunately is only available for Windows.
This chapters details the sensors used in the hub-based system that was designed for use with D-mode receivers. See the next chapter, S.Port Sensors, for a discussion of the new S.Port-based system that is designed to be used with X-mode sensors.
In most scenarios the telemetry setup requires at least three components:
- a receiver with a data port
- the sensor hub FSH-01
- one or more sensors
The sensors connect to the sensor hub and the sensor hub connects to the receiver's data port. The FBVS-01 voltage sensor is the only purely analog sensor and it connects directly to the receiver without going through the sensor hub.
FrSky offers the following sensors.
FBVS-01 Battery Voltage Sensor
The FBVS-01 is a simple, low cost voltage sensor. It only reports one voltage and can be connected to any receiver with an external analog port. Most commonly this will be the A2 port, but on receivers equipped with an external A1 port (currently only the D8R-II plus and D8R-XP) two sensors can be used simultaneously.
The FBVS-01 must not be confused with the FLVS-01 Lipo Voltage Sensor (see below).
You will want the FBVS if you want to monitor an external battery source. This is common on electric aircraft as the receiver is supplied power by a BEC circuit in the speed control. If this is your situation, then you can connect the FBVS to the A2 port on your telemetry receiver. If your receiver does not have an A2 port (X8R), then you can connect to the volt port on a hub. Now connect the red wire on the other side of the FBVS to whatever voltage source you would like to monitor. This might be a single cell from the flight pack, or all of the cells on the flight pack. Most common connection is to solder the red wire onto the positive wire going into your speed control. This will give you your full pack voltage. If you only want to check a single cell, then you can connect into the first positive cell of your balance port for the battery. (If you are using an FLD-02 LCD screen to check your voltages or sound an alarm and are flying different cell count packs from plane to plane (3 cell and 4 cell) it is easier to monitor just a single cell on a battery pack, otherwise you would need to change your voltage alarm value every time you fly a different sized pack.
FLVS-01 Lipo Voltage Sensor
|Cell Voltage Display Range||0.20-4.20V|
|Voltage Display Resolution||0.01V|
|Voltage Detection Precision||0.03V|
|Display||128x64 OLED display|
The FLVS-01 is a more advanced voltage sensor than the FBVS-01. It is a digital sensor reporting individual cell voltages for 1s through 6s batteries. It can operate connected to a sensor hub FSH-01 or alternatively can be connected to one of the FAS-40/100 current sensors which in turn connect directly to the receiver. In either case it can only be used with receivers that have a digital data port (all "D"-series receivers except the DF6R). It reads cell voltage via the battery balance plug.
Two of the sensors can be combined for battery packs of up to a 12s configuration. Beware that with the current V2.01 firmware the FLD-02 telemetry display can only display 6 voltages.
A nice feature is the integrated OLED display that enables the FLVS-01 to be used as a standalone lipo checker.
FLVS-02 Lipo Voltage Sensor
The FLVS-02 is a cheaper and lighter version of the FLVS-01. It does not have the integrated OLED display. Other than that it operates the exact same way.
FAS-40 Current Sensor
|Maximum Safe Current||40A|
|Sensor Current Consumption||20mA|
The FAS-40 is a current sensor with a maximum rating of 40 Amps. It comes without power connectors, the user is required to solder suitable power connectors to the wires or solder it directly into the model's wiring.
Being a digital sensor the FAS-40 can only be connected to a receiver equipped with a digital data port. It can be connected directly - without going through the FSH-01 sensor hub - if no other digital sensors are to be used. One or two digital voltage sensors FLVS-01 or FLVS-02 can be connected to the FAS' voltage port (daisy-chained). In this configuration the FAS will report both current and voltage via its digital data port to the receiver.
FAS-100 Current Sensor
|Maximum Safe Current||100A|
|Sensor Current Consumption||33mA|
The FAS-100 is the equivalent to the FAS-40 but rated for 100 Amps current. It can be purchased with either Deans-T or XT-60 connectors or without connectors. It is physically larger and heavier than the FAS-40 but otherwise works the same.
FGS-01 Fuel Gauge Sensor
This is a digital fuel sensor that attaches to the outside of (non-metallic) fuel tanks. 5 fuel levels between empty and full are reported. It requires the sensor hub FSH-01 to operate.
GPS-01 GPS sensor
As the name implies the GPS sensor reports the model's position coordinates to the receiver via the FSH-01 sensor hub.
FVAS-01 Variometer Sensor
This is the original altitude/variometer sensor. It will operate between 0 and 9000m ASL, has a resolution of 1m, and needs the FSH-01 to operate. Its mounting position needs to be well chosen as wind hitting the sensor influences the readout precision. In addition to the sensor itself not being very precise, the long cable introduces signal noise into the sensor reading, especially if physically located close to the receiver antenna. This can be minimized by shortening the cable as much as possible and locating it far away from all over electrical components.
Using the FVAS-01 sensor with the FLD-02 has distinct drawbacks, see the FLD-02 chapter for an explanation. In general, the FVAS-02 sensor (see below) is by far preferable.
FVAS-02 Variometer Sensor
Information on this new sensor by Frsky is extremely sketchy. It seems like the sensor was released without any internal coordination and especially without updating the documentation. Much of the content of this chapter was pieced together from forum posts and reverse engineering by people who actually have a sensor and disassembled and/or tested it. See especially this two-part test by user "mihlit" on RCGroups.com here and here.
The newer variometer sensor FVAS-02 reports altitude readings and climb/sink rate. It is a hubless sensor meaning it can be connected directly to the receiver's digital data port or via the sensor hub FSH-01 if it is to be used in conjunction with other sensors. It can operate between -700 and 10000m (-2,300 to 32,800 feet) with a 10 cm (3.9") resolution. The most common use is as a lift indicator to glider pilots.
There are two versions of this sensor available: the FVAS-02 and the FVAS-02H (for High precision). They are exactly the same except the FVAS-02H uses a higher-quality barometric sensor which gives more precise readings. The two products are externally indistinguishable. If you are buying a used sensor not in its original unopened packaging, there is no way of knowing which one you are getting short of opening up the shrinkwrap and identifying the chip on board. The chip in the normal sensor carries the label "M3PR WZ0C" while the high-precision one is labeled "561101BA01 532194Z".
At the time of this writing FrSky has not published official information on this sensor on their website. However, various online retailers provide the sensor instructions. Google for "frsky fvas-02h" and follow the links to the "BRC Hobbies" or the "my-rc.ch" websites to find them as a downloadable PDF linked in the product description.
Connecting the FVAS-02
The new variometer FVAS-02 has two types of output. It puts out digital altitude values as a number on the data pins and also an analog variation voltage (climb/sink) on the analog pin. It can be used with current 8-channel D-mode series receivers with a data port - “old” generation - and the upcoming X-mode receivers for the Taranis and XJT module - “new” generation.
It has two types of connector.
- Two of the older white 4 pin Data Connector (JST 1.5mm type) which use the data protocol of existing FrSky sensors and the sensor hub (labeled Data In and Data Out).
- Two of the newer 3 pin Smart.Port connector, which will be used by the new generation of receivers and sensors (starting with the X8R receiver). They have the same standard 3-pin 0.1” connector spacing as a servo.
These two types of connections are not interchangeable but the vario can internally convert one to the other so that it can be used to join “old” Data and “new” SmartPort devices. When using the “old” data port, only altitude data is available as a digital value; lift/sink rate is available as an analog voltage only. When using the “new” S.Port both altitude data as well as lift/sink rate are available over the digital protocol.
- Altitude: The absolute altitude is calculated from barometric pressure and is sent as a number from the data pins on both connectors. This is the S pin on the SmartPort connector and the Tx pin on the upper data connector
- Variation: The rate of change of altitude appears as a voltage on the DA pin only of the upper (Data Out) data connector.
In addition, the vario requires supply voltage and ground connection, which is done through two more pins on the connectors. All 4 connectors have V+ and GND pins. The SmartPort uses the same wiring convention as a servo, that is center pin for V+.
In order to connect to both "D-mode" and "X-mode" receivers FrSky provides 3 cables with the vario. You only use one of these depending on the setup.
- a three wire cable with 3 pin black servo connectors on each end which will be used with “new” X-mode receivers and sensors as they become available. Can connect to either SmartPort connector – they are identical - and there are two to allow daisy chaining of additional devices.
- a 4 wire cable with white 4 pin JST connectors on each end. This joins the vario to the FSH-01 Hub or a FAS-40/100 current sensor, which is then connected to a receiver and other sensors in the “old” style.
- a special cable with a white JST on one end and three black connectors on the other that allows direct connection to a D8 series receiver. This avoids having to use a data hub. The FAS40/100 current sensor can then be plugged into the vario as well to make a compact current, capacity and vario/altitude telemetry system. One connector is a 3 pin servo sized plug with only two wires and is connected to any spare channel on the D8 to supply V+ (red wire) and GND (black wire) to the vario. The two single connectors are plugged into the digital data Rx pin (Yellow wire) and the analog DA (either A1 or A2) pin (Brown wire) on the side of the D8 receiver. Note the official Frsky documentation that comes with the variometer (and is available as a download on their website) incorrectly specifies the yellow wire should go to the Tx pin.
If the variometer is being used with a Turnigy 9x or 9XR radio with the telemetry modification made to it's main board, the brown wire is left disconnected.
The FVAS-02 sensor can be used with the DFT, DJT, DHT and DHT-U to give audible variometer indication, something that wasn't possible with the old FVAS-01 sensor. Use the above-mentioned special cable with the white JST on one end and three black connectors on the other to connect the sensor to the receiver.
The FVAS-02 variometer sensor outputs a voltage of 1.65V via the brown wire towards the DA port when it is stationary (i.e., the altitude reading doesn't change). This is the midpoint of the maximum possible 3.3V (or in digital terms a value of 127 for an 8 bit value). An increasing altitude reading results in the voltage increasing proportionally to the rate of climb; a decreasing altitude reading will result in a proportionally decreased voltage reading.
Using this information it is straightforward to enter the two alarm thresholds with separate beep alerts, e.g. A2_1 at less than 125 with one beep and A2_2 at greater than 129 with two beeps. See Alarms for more information.
Using the vario sensor with an FLD-02 with firmware version 2.1 or above will display a vertical bar on the screen showing lift and sink. This feature is not available with the DHT-U even with the current firmware version 2.3.
Bridging between S.Port and "old style" Data Port
The FVAS-02 can also serve as a bridge between a receiver's S.Port and a sensor hub. An FSH-01 sensor hub can be connected to the FVAS-02 via the "Data In" port. Values of sensors connected to the FSH-01 hub will be sent out over the S.Port to the S.Port-equipped receiver. Instead of the FSH-01 a FAS-40 or FAS-100 current sensor can also be directly connected (see the FAS sensor description for more information).
Note: early documentation for the FVAS-02 sensors indicated the sensor would also be able to bridge S.Port sensor data to D8-mode receivers, thus allowing future S.Port sensors to be used on the D8-mode receivers. This function is not in fact supported by the FVAS-02 sensors. Frsky has since updated the documentation to remove advertisement of this feature.
Using the FVAS-02 with the D4R-II Receiver
The FVAS-02 sensor ships with cables that allow it to be attached to the "D-mode" 8-channel receivers. The supplied Y-cable will not physically fit the D4R-II receiver which uses 1.27mm pitch JST connectors instead of the 1.5mm pitch JSTs on the 8-channel receivers. You need to make up a suitable cable using the cables supplied with the D4R-II receiver. User jj604 has described the configuration he used and took the accompanying pictures.
The above picture shows the FVAS-02 with the supplied Y-cable and the D4R-II receiver with the supplied mini-JST cable. The latter needs to be modified in the following way:
- Lift the little tab on the smaller of the two white JST connectors (the D4R-II end) that holds the white wire that is not connected at the other end. Remove and discard the White wire.
- Swap the Brown wire on the smaller JST connector into the hole the white wire just came out of.
Using this modified cable you can connect the "Data Out" port on the FVAS-02 to the D4R-II as shown in the following diagram:
Note: At least two different wiring colors have been reported for the data cable included with the D4R-II. Some are White, Yellow, Brown, Black as shown here and others are White, Green, Red, Black. The following picture of the completed connected cable shows where each wire connects to make sure there is no confusion.
Note white heat shrink tubing on unused S.Port connector at top left to prevent accidental in-flight short circuit on the exposed pin carrying 5V.
Now all that is left to do is supply V+ to the sensor. The cleanest solution would be by inserting a connector and red wire from one of the cables supplied with the vario sensor into the blank fourth slot on the sensor connection as shown in the diagram.
An easier way to supply V+ is shown in the following diagram, by plugging into one of the channels on the receiver. However, this will essentially reduce the D4R-II to only a 3-channel receiver.
Alternatively, you can connect to any of the other three positive connectors on the sensor (one in the "Data In" port and two in both S.Port connectors) with a single V+ wire from anywhere in the plane, preferably directly from the BEC or ESC.
Using the FVAS-02 with the D6FR Receiver
The D6FR receiver does not have a digital data port, but it does have an externally accessible analog A2 port. The FVAS-02 vario can be used with this receiver by connecting the brown DA wire to A2 and the power connector into a servo plug. The D6FR will transmit variation (lift/sink) information in the same way as the D8 receivers, but it will not transmit digital altitude information. The DHT-U as well as 9X/9XR transmitters modified for FrSky telemetry information display the variation information. The FLD-02 also displays this information, but the DHT-U and FLD-02 use different screen layouts. The FLD-02 lacks a graphical display of variation with the D6FR and shows only the variation voltage. See the Telemetry in Gliders section for a detailed explanation.
A specialty of the D6FR receiver is the fact that the center pin on the DA port has +5V. This means that the FVAS-02 can be powered off of that port instead of blocking a free servo port for the power connection. For this purpose the brown pin of the single connector needs to be moved into the third pin of the power connector (the 3 pin connector that only has one red and one black wire connected to it). See picture below. Then plug that 3 pin connector into the A2 port on the receiver.
Note: this cable can only be used with a D6FR, it will not work with a D8 receiver!
Using the FVAS-02 on Telemetry-modified 9X with ER9X firmware
The built-in telemetry displays altitude in ft or m by setting imp (imperial) or met (metric) page 9/11 (Telemetry) of the model setup. Also make sure that the option is set to "FrHub" (when connecting FVAS-02 directly to receivers, I don't know how it functions if someone has a hub in between)otherwise data is corrupted. When the transmitter is switched on it displays absolute altitude. When the menu button is pressed while in the telemetry display page, it then switches to relative altitude using that altitude as reference. Switching back to absolute altitude requires turning the transmitter off and on.
It displays voltage for A2, which is vertical speed (variation). The value depends on the reference value entered (for example if the reference value is 10.0v, then the display shows 5.0 as mid value (no vertical speed). It will go above 5.0v when climbing and below when descending. Alarms can be set for values (for ex 4.9 and 5.1) to indicate sink and lift respectively.
To get the transmitter and the DJT module to beep, make sure that the "Int. Frsky alarm" is set to "off" in the Tx setup page 1/6. If set to on, neither will beep (but the vario tone below still works)
Following is an option to have a vario tone other than the regular alarms. It comes on top of the alarms if these are set up:
- On page 10/11 (Telemetry2) of the model setting do the following (it's at the bottom of the options, so scroll down all the way)
- Set “Vario: Source” to A2. That seems to be more sensitive and exact. It takes the value from the data I presume. If set to vspd (Vertical Speed I presume) it works as well but I assume it's computing the value from altitude with a timer. It seems less accurate in this case (I presume it's to create a vario tone from GPS data). In case of D6FR, only A2 would work, since there is no altitude available (a presumption, not checked yet).
- “Switch” will set up a switch to turn it on. If no switch is selected, there is no vario tone.
- “Sensitivity” (between 0 and 50). Doesn't seem to make a big difference, 30 is a good value it seems.
- “No Sink Tones” “off” will give you a certain tone for climbing and a different tone for descending. The two are fairly distinctive, so it's easy to know what is happening.
If “No Sink Tones” is set to “on” then there is no tone while descending (as expected) a slow tone as staying at altitude and an increased tone for rising.
There is also an option on that same page for setting up a max altitude: “AltAlarm” if set, will give you an alarm when the altitude reaches either 122 or 400 (of whatever the altitude is, if it is in feet, then either 122 feet or 400 feet, if meters, then 122M or 400M). There is no other value available (as of version 803) and it cannot be changed.
This setup works with all the "D"-mode receivers - the D4R-II, D6FR, D8R-II plus, and D8R-XP.
The first version of the FVAS-02 had a bug in the firmware that led to the variometer locking up after several minutes of flight. Unfortunately, the bug cannot be found by bench testing the sensor (leaving it connected for a time without actually flying the plane). The plane needs to be flown with varying altitude readings for anywhere from 3 to 8 minutes. The sensor will then lock up and not report any more altitude readings.
A new firmware has been issued that corrects the problem. With the FVAS-02 not yet listed on the FrSky website, the firmware cannot be easily found. This is the download link: http://www.frsky-rc.com/download.asp?id=22 FrSky states that all FVAS-02 delivered to dealers after May 1st 2013 should already have the new firmware installed, but there is no external documentation of the firmware revision on the sensors.
Note that with the FVAS-02 being an S.Port sensor, you need a specially modified USB cable to do the firmware upgrade. Please see the S.Port Sensor Firmware Upgrades section for further details and a cable schematic.
TEMS-01 Temperature Sensor
The temperature sensor reports temperatures between -20 and 250 degrees Celsius (-4 to 482 degrees Fahrenheit) with an accuracy of 1 degree C. It needs the sensor hub FSH-01 to operate. Up to two sensors can be connected to the hub simultaneously. Internally it is a 100K NTC (Negative Temperature Coefficient) thermistor. The resistance of the thermistor is 100K at 25 degrees C and the resistance goes down as the temperature increases - hence the designation negative temperature coefficient. If you are going to use an aftermarket sensor, be sure it's a 100K NTC.
RPMS-01 RPM Sensor
An optical sensor capable of reading head and propeller speeds up to 60,000rpm. Requires the FSH-01 sensor hub.
TAS-01 Triaxial Acceleration Sensor
Commonly called a G-sensor it reports acceleration separately for the tree different axes. The measurement range is -8G to +8G (G = 9.8m/s2) with an accuracy of 0.016G. Connection via the sensor hub FSH-01.
FrSky is releasing a new line of hubless sensors that are equipped with S.Port connections. The FVAS-02 variometer sensor is the first one released, more are expected to follow. The possibility of daisy chaining the sensors together without having to use the FSH-01 sensor hub is the most compelling reason to use this new generation of sensors.
Compatibility with "D mode" receivers
"D mode" receivers are not equipped with an S.Port. Currently the only way to connect S.Port sensors to those receivers is to use an FVAS-02 variometer sensor which can bridge (translate) between the S.Port and Data Port protocols in both directions. See that sensor's description for more information.
S.Port Sensor Firmware Upgrades
The new sensors are updated through their S.Port connection. The previously-used FrUSB-3 USB adapter cable predates the S.Port and cannot be used in its stock form. Until a replacement product is released users have to make their own cable. User 'mihlit' describes the process as follows:
Basis for the cable is either the FrUSB-1 or FrUSB-3. Make sure the wires are in this order: black, red, yellow, brown. The first three wires (black, red, yellow) go to one S.Port. The remaining brown wire goes to the signal ('s') pin of the second S.Port through a diode (1N4007) with the ring on the diode pointing to the 's' pin.
- plug the FrUSB-3 into a USB port on your computer
- connect the brown wire (through diode to 's' pin on S.Port)
- start the firmware update software
- select correct com port
- open the file with the sensor firmware
- now the software starts searching for the sensor to update
- connect the plug with the three wires to the other S.Port
- once the software recognizes the sensor, click "Download"
- wait until the update finishes
The official FrSky documentation for the cable in the diagram below shows both the RxD and TxD connections going to the same S.Port but the procedure given above has been verified to work and seems simpler.
The sensors have exposed male S.Port connectors which carry 5V on them. It is recommended to either put a blind plug or a short length of heat shrink tubing on unused connectors to prevent a short circuit in-flight with potentially disastrous consequences.
This sensor is described in much detail in the hub-based sensors chapter.
FAS-40S Current Sensor
This is a 40A current sensor equipped with the S.Port interface. This sensor was originally announced as the FCS-40A. It comes standard with XT60 connectors on both ends.
FAS-100S Current Sensor
Announced for January, 2014 this is the 100A-rated equivalent to the FAS-40S.
SP2UART Analog Adapter
This adapter provides two analog connectors, e.g. for the FBVS-01 analog voltage sensors. The analog values are digitally transmitted via the S.Port bus. This adapter is mostly useful in conjunction with the X8R receiver which does not feature analog inputs, or with any D16-mode receiver if additional analog ports are required.
Released in November, 2013 this device can be considered an answer to the need demonstrated by the success of the X8R2analog third-party voltage sensor (which is different in that it is more than just an adapter).
FLVSS Voltage Sensor
This is a 6s lipo voltage sensor equipped with the S.Port interface, connecting to the lipo balance plug. It is available as of November, 2013.
The sensors feature a user-settable 4-bit ID, thus resulting in an address space for 16 sensors. The IDs can be set either using a PC software program or via the Frsky Smart Dashboard.
A maximum of 16 such sensors can be connected to the same S.Port bus to monitor individual packs, but a maximum of two of the FLVSS sensors can be connected together for monitoring of up to 12-cell pack voltage information. So for example, two sensors could monitor a 12s flight battery, while a third sensor would monitor a separate 2s receiver pack.
GPS (FrSky GPS V2 for S.PORT)
This is a new GPS sensor for the S.Port telemetry system. Availability has been announced for December, 2013.
Air Speed & RPM Sensor
This is a new sensor for measuring air speed and motor/pro rpm. Availability has been announced for February, 2014.
Third Party Sensors
S.Port sensors are also being developed by independent third parties. Here's an overview of the products currently available or being released.
X8R2analog A2 Voltage Sensor
A group of people around RCGroups.com user aadamson has been developing this sensor which fills a significant void in the Frsky S.Port telemetry system -- the lack of a small, cheap, light flight pack voltage sensor similar to the FBVS-01 in the hub sensor system. Named the "X8R2analog" device is available via direct order, and also in the USA from Aloft Hobbies via their website http://www.alofthobbies.com/x8r2analog.html and in Europe via T9 Hobbysports http://www.t9hobbysport.com/ .
Pack voltage picked up by this sensor is displayed as the A2 analog voltage value on all types of telemetry displays, whether its internal on the Taranis or external on the DHT-U or FLD-02. It is available with the receiver operating in either the D8-mode or the D16-mode.
Note that this sensor should be physically the last one on the S.Port bus as protocol pass-through isn't available (yet).
The manual for the sensor can be found here: http://www.rcgroups.com/forums/showpost.php?p=26586566&postcount=1
Example Use Cases
This section describes use cases of telemetry that have been successfully tested by users. Feel free to submit your own experiences and please be as detailed as possible regarding hardware and software revisions that you use.
If you are a member of RCGroups feel free to also post your use case to the thread FrSky 2.4Ghz - Telemetry Hub & Sensor discussion.
Flight Pack Voltage Measurement
Measuring flight pack voltage is both simple and hard: simply connect a suitable voltage sensor (either the cheap FBVS-01 or the more advanced lipo sensor FLVS-01/-02) to the receiver and configure alarms to suit. The FLVS-sensors are digital sensors, while the FBVS-01 is an analog sensor that is much simpler in construction but harder to configure. To do that first we need to understand how analog voltage sensors work.
The voltage measurement inputs (A1/A2) of the FrSky receivers have a maximum measuring range of 3.3V. If the voltage to be measured is higher, that voltage needs to be divided by a ratio to bring it under 3.3V. The concept is simple, essentially just two resistors. For those interested in the theoretical background this Wikipedia article has some good information: http://en.wikipedia.org/wiki/Voltage_divider
Inside the Frsky voltage sensors (FBVS-01 or FLVS-01) there is a cascading chain of resistors with 1k5 Ohms value allowing to obtain various ratios for different voltage ranges: 1/2, 1/4, 1/6. These division ratios should be used with various battery pack configurations as follows:
- 1s use 2:1 (maximum voltage measurable: 2*3.3V = 6.6V, enough for 1s)
- 2s use 4:1 (maximum voltage measurable: 4*3.3V = 13.2V, enough for 3s)
- 3s use 6:1 (maximum voltage measurable: 6*3.3V = 19.8V, enough for 4s)
So, assuming we want to measure a 4s LiPo (with a maximum charged voltage of as much as 16.8V) we must use a divisor of at least 16.8/3.3 = 5.1 times. Frsky allows only integer divisors so we will choose the next integer ratio, 6. This matches the list given above.
The resistor values for 6:1 divisor must be in a 1/5 ratio according to the formula from Wikipedia. It is simple to remember:
resistor ratio = (divisor ratio - 1)
So any resistor pairs like 2k and 10k or similar are perfect for this task. These resistors are integrated on the FrSky voltage sensors' boards. If you want to measure higher voltages you would need to source a third-party sensor or, with the above information, build your own using a custom division ratio.
Note that the internal voltage sensors in the D8-mode receivers use a division ratio of 4:1, so when using them (default on the D4R-II and D6FR, or when so jumpered on the D8R-II+ and D8R-XP) set the A1 display ratio on the FLD-02 or DHT-U to "4".
Voltage alarms can be configured on both the FLD-02 and DHT-U display units. Note that the voltage division ratios must be configured to be the same values as on the voltage sensor, otherwise the display will show and sound alarms at wrong values! In other words: if your voltage sensor uses 6:1, set the display unit to 6:1 also.
To set these alarms using the toggle rocker go to "Menu", then to the "Alarm Set" field. Pressing the button multiple times you will cycle through the 6 alarms that can be set: two levels of alarms for each voltage input, and two RSSI. Read the RSSI chapter for the RSSI alarm configuration. To set the voltage alarms, you select either A1_1 or A1_2 if your sensor is connected to the A1 receiver port, or A2_1/A2_2 if it is connected to the A2 port.
After choosing one of those alarms, go to the row below and choose:
- the alarm sound - 0 = none 1,2,3 different alarm levels
- select if you want the alarm if the measured value is above or below the threshold (below is almost always correct to monitor battery voltage)
- the alarm value (the confusing part)
It is important to understand that the alarm value is not a voltage, but a digital computer value. The formula of this value is:
alarm value = pack voltage / ratio / 3.3 * 255
Note that the alarm value is not a "per cell" alarm, it is calculated from the pack voltage.
For example, to set alarm for a 3s pack at 10.5V, the value will be:
10.5 / 6 / 3.3 * 255 = 135
After filling in the three fields above, press OK to store the alarm in the module. This must be done individually for all of the 4 voltage alarms if you want to set all of them. If you only have a single voltage sensor connected to one of the A ports, set only the two alarms for that port (either A1 or A2).
User jj604 has created an Excel sheet that can be used to calculate these alarm values. You can download it from here: . An online version which can also be used with a smartphones at the field can be found here: .
Power Consumption and Voltage Measurement
The following setups are examples, in increasing level of complexity, of monitoring battery conditions.
Monitoring 1 Battery without Sensor Hub
The battery cell voltage is monitored by the FLVS-01 which is connected to the current sensor FAS-40 or FAS-100. The FAS in turn connects directly to the data port on the receiver. This setup is cheap, light, and low on power consumption.
Monitoring 2 Battery Levels without Sensor Hub
This setup is able to monitor two batteries, e.g. the main flight pack and a battery used for the camera that records the flight. It expands on the previous example by adding an analog FBVS-01 voltage sensor for the second battery. The sensor connects to the A1 or A2 port on the receiver.
Monitoring 2 Battery Levels with Sensor Hub
Should you wish to add another sensor - e.g. a GPS sensor - to the above setup it becomes necessary to add a sensor hub FSH-01 because the two digital sensors cannot share the single data port on the receiver.
Telemetry in Gliders
All of the FrSky telemetry receivers can be used in EP or straight gliders. You should select the proper receiver by analyzing your use case first.
- the D6 can send only receiver voltage plus one analog input voltage – either from an FBVS-01 battery voltage sensor or the variation signal from the new FVAS-02 vario. It cannot send numerical (digital) information such as altitude, current etc.
- the D4R-II can send receiver voltage plus one analog input voltage – either from an FBVS-01 battery voltage sensor or the variation signal from the new FVAS-02 vario. It can also send numerical (digital) information such as altitude, current etc. If you want pack voltage plus variation you need to use an FLVS-01, which sends digital data, for the pack voltage.
- the D8 receivers can send two separate analog voltages. One could be receiver voltage (using the jumper) and the other the pack voltage (using an FBVS-01) but the most useful combo for power gliders may be pack voltage using an FBVS-01 on A1 and variation voltage from the vario on A2. If you have the pack voltage and are using a BEC then receiver voltage is redundant information. For pure gliders, receiver voltage and variation would be attractive.
- the X8R receiver can send digital voltage information from an FLVS-01 or -02 digital voltage sensor, digital receiver voltage, and fully digital altitude and variation (lift/sink) information from the FVAS-02.
The D4, D8, and X8R series also send numerical (digital) information such as altitude, current etc. Numbers such as altitude, current and so on are sent from the sensors via the FSH-01 Sensor hub to the D4 and D8 receivers data port with a couple of useful exceptions. The new vario and the Ampere sensors can connect directly and do not require a hub.
For electric fliers some obvious non-hub combos for the D4 and D8 are a current sensor in the data port and an FBVS-01 in the A2 port, or for the D8 an FBVS-01 for pack voltage in A1 and a vario plus current sensor in the data port for Amps and altitude plus the variation in A2. The Ampere sensor will also accept FLVS-01 voltage sensors without the need for a hub.
The usefulness of A1 and A2 is that audio alarms can be set for two values of both. So you could have a low pack alarm at two levels plus a tone for sink and another for climb.
Example Display - FLD-02 - D8 receiver and pack voltage and vario
The D4 will show the same display as the D8 except that only receiver voltage can appear in the A1 window.
Example Display - FLD-02 - D6 receiver and vario
Example Display - DHT-U - D8 receiver and pack voltage and vario
The DHT-U has no visual variation bar display. Also the A1 and A2 voltages appear on separate screens. Audio alarms can be set just as with the FLD-02 however. Absolute and relative altitude is switched by the left hand top button on the unit.
Example Display - DHT-U - D6 receiver and vario
To Be Done.
- The Frsky RC website and their own Frsky RC forum.
- RCGroups FrSky 2.4Ghz - Telemetry Hub & Sensor discussion board.
Suppliers of FrSky equipment
- Asia: Hobby King
- Europe: Intermodel, AvioMotive, Microtechnics, Giantshark, T9 Hobby Sport
- North America: Aloft Hobbies
Large parts of this Wiki contain collected and cross-referenced information from FrSky and FrSky resellers available via their websites. Additional information provided through own observations and other users' experiences.
In addition to the authors listed in the history of this Wiki significant contributions of material have been made by RCGroups users jj604, renatoa, kilrah, mihlit, and Michael V.